This invention relates to magneto-optical recording media including a magneto-optical disk, a magneto-optical tape, and a magneto-optical card adopted for a magneto-optical recording/reproducing device, and further concerns a reproducing device thereof.
Conventionally, as a rewritable optical recording medium, a magneto-optical recording medium has been put into practical use. Such a magneto-optical recording medium has the drawback of degrading reproducing property when a diameter and spacing of a recording bit, that serve as a domain, become smaller relative to a beam diameter of a light beam, that is emitted from a semiconductor laser and is converged on the magneto-optical recording medium.
Such a drawback is caused by an adjacent recording bit which enters the beam diameter of the light beam converged on a desired recording bit so that individual recording bits are not separately reproduced.
In order to overcome the above-mentioned disadvantage, Japanese Published Unexamined Patent Application No. 320134/1997 (Tokukaihei 9-320134, published on Dec. 12, 1997) discloses a magneto-optical recording medium shown in FIGS. 30 and 31. The magneto-optical recording medium has a construction in which a reproducing layer a1 and a recording layer a4 are stacked via a non-magnetic intermediate layer a3. The reproducing layer a1 is in a state of in-plane magnetization at room temperature and enters a state of perpendicular magnetization at higher temperatures. The recording layer a4 is made of a perpendicularly magnetized film. In the magneto-optical recording medium which has a magnetostatic combination of the reproducing layer a1 and the recording layer a4, an in-plane magnetization layer a2 is formed so as to be adjacent to the reproducing layer a1. With this construction, in a region whose temperature is lower than the Curie temperature in the in-plane magnetization layer a2, it is possible to firmly fix the magnetization direction of the reproducing layer a1 at an in-plane direction, that is horizontal to the film surface. In a region whose temperature is not raised by irradiation of a light beam a5, namely, in a region whose temperature is lower than the Curie temperature in the in-plane magnetization layer a2, the reproducing layer a1 enters a state of complete in-plane magnetization so as to mask a recording domain a9.
Meanwhile, the reproducing layer a1 is in a perpendicular magnetization in a region which is irradiated with light beam up to more than the Curie temperature in the in-plane magnetization layer a2. The perpendicular magnetization direction of the reproducing layer a1 is allowed to correspond to a direction of leakage flux appearing in the recording layer a4 so as to transfer a recording domain a8 of the recording layer a4 onto the reproducing layer a1; thus, it is possible to reproduce merely the recording domain a8 which exists inside a light beam spot a6.
Here, the reproducing layer a1 needs to have in-plane magnetization at room temperature and enter a state of perpendicular magnetization at higher temperatures; therefore, unlike a compensation composition in which magnetic moment of a rare-earth metal(RE) and magnetic moment of a transition metal(TM) balance each other, RErich composition containing a large amount of rare-earth metal is necessary. Hence, in the reproducing layer, the transition metal(TM) moment and total magnetization oppose each other, and as shown in FIG. 31, TM moment and leakage flux are arranged in opposite directions in a region a7 which is raised in temperature.
As described above, the recording domain a8, which has merely an area raised in temperature, is transferred onto the reproducing layer a1 prior to reproduction, so that it is possible to reproduce a signal recorded in a period, which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce.
However, upon reproduction using the conventional reproducing medium, when the recording domain a8 becomes smaller, a domain all transferred to the reproducing layer a1 also becomes smaller, resulting in reduction in intensity of a reproduction signal.
The objective of the present invention is to provide a magneto-optical recording medium and a reproducing device that reproduce a signal recorded in a period, which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce, without reducing an amplitude of the reproduction signal.
In order to achieve this objective, the magneto-optical recording medium of the present invention includes a reproducing layer which has perpendicular magnetization from room temperature to the Curie temperature in a single layer, an in-plane magnetic layer which has in-plane magnetization from room temperature to the Curie temperature, and a recording layer which has perpendicular magnetization from room temperature to the Curie temperature, wherein Tc2 less than Tc1 and Tc2 less than Tc3 are satisfied, where Tc1 represents the Curie temperature of the reproducing layer, Tc2 represents the Curie temperature of the in-plane magnetic layer, and Tc3 represents the Curie temperature of the recording layer; and the reproducing layer includes an area which has a temperature of less than Tc2 and has in-plane magnetization due to an exchange coupling with the in-plane magnetic layer, and an area which has a temperature of more than Tc2 and has single-domain perpendicular magnetization due to expansion and transfer of magnetization information from the recording layer to the reproducing layer.
With this arrangement, magnetization information recorded in the recording layer is expanded and transferred to an area whose temperature is more than Tc2 in the reproducing layer, so that a large single domain is formed in the reproducing layer. Hence, even in the case when small bit information is recorded in the recording layer, a domain reflecting the bit information is expanded to the reproducing layer. Further, as described above, in the reproducing layer, a domain reflecting a specific bit information is expanded, so that a reproduction signal becomes less prone to the influence of a bit located around the specific bit. Therefore, even when a signal is recorded in the recording layer in a period which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce, it is possible to reproduce the signal without reducing an amplitude of the reproduction signal.
Moreover, the magneto-optical recording medium of the present invention includes the reproducing layer which has perpendicular magnetization from room temperature to the Curie temperature, in a single layer, the in-plane magnetic layer which has in-plane magnetization from room temperature to the Curie temperature, and the recording layer which has perpendicular magnetization from room temperature to the Curie temperature, wherein Tc2 less than Tc1 and Tc2 less than Tc3 are satisfied, where Tc1 represents the Curie temperature of the reproducing layer, Tc2 represents the Curie temperature of the in-plane magnetic layer, and Tc3 represents the Curie temperature of the recording layer; and the reproducing layer and the recording layer have maximum total magnetization values at a temperature higher than Tc2.
With this arrangement, at a temperature higher than Tc2, in an area whose temperature is nearly a temperature where total magnetization of the reproducing layer and total magnetization of the recording layer reach maximum values, a heating operation is performed so as to include merely a single bit recorded in the recording layer; thus, leakage flux appearing merely from the bit can be magnetostatically coupled to magnetization of the reproducing layer whose temperature is more than Tc2. Therefore, it is possible to form a large domain in the reproducing layer merely in accordance with a magnetization direction of a single bit that is recorded in the recording layer, so that even when a signal is recorded in the recording layer in a period which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce, it is possible to reproduce the signal without reducing an amplitude of the reproduction signal.
Further, the reproducing device of the present invention for reproducing magnetization information recorded in the magneto-optical recording medium, the magneto-optical recording medium including a reproducing layer which has perpendicular magnetization from room temperature to the Curie temperature, in a single layer, an in-plane magnetic layer which has in-plane magnetization from room temperature to the Curie temperature, and a recording layer which has perpendicular magnetization from room temperature to the Curie temperature, wherein Tc2 less than Tc1 and Tc2 less than Tc3 are satisfied, where Tc1 represents the Curie temperature of the reproducing layer, Tc2 represents the Curie temperature of the in-plane magnetic layer, and Tc3 represents the Curie temperature of the recording layer; and the reproducing layer includes an area which has a temperature of less than Tc2 and has in-plane magnetization due to an exchange coupling with the in-plane magnetic layer, and an area which has a temperature of more than Tc2 and has single-domain perpendicular magnetization due to expansion and transfer of magnetization information from the recording layer to said reproducing layer, the reproducing device being provided with a light emitting means for emitting light on the magneto-optical recording medium and a light receiving means for receiving light reflected from the magneto-optical recording medium, wherein upon reproduction, the light emitting means emits light on the magneto-optical recording medium so as to heat the in-plane magnetic layer to more than the Curie temperature.
With this arrangement, in the magneto-optical recording medium, magnetization information recorded in the recording layer is expanded and transferred to an area, whose temperature is increased to more than Tc2 by the light emitting means in the reproducing layer. Namely, a large single domain is formed in the reproducing layer; thus, even when a small bit information is recorded in the recording layer, a domain reflecting the bit information is expanded in the reproducing layer so as to improve intensity of a signal which is obtained by the light receiving means for receiving light reflected from the magneto-optical recording medium. Also, as described above, in the reproducing layer, a domain reflecting a specific bit information is expanded, so that a reproduction signal becomes less prone to the influence of a bit located around the specific bit. Therefore, even when a signal is recorded in the recording layer a period which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce, it is possible to provide a reproducing device which can reproduce the signal without reducing an amplitude of the reproduction signal.
Further, the reproducing device of the present invention for reproducing magnetization information recorded in the magneto-optical recording medium, the magneto-optical recording medium including the reproducing layer which has perpendicular magnetization from room temperature to the Curie temperature, in a single layer, and the in-plane magnetic layer which has in-plane magnetization from room temperature to the Curie temperature, and the recording layer which has perpendicular magnetization from room temperature to the Curie temperature, wherein Tc2 less than Tc1 and Tc2 less than Tc3 are satisfied, where Tc1 represents the Curie temperature of the reproducing layer, Tc2 represents the Curie temperature of the in-plane magnetic layer, and Tc3 represents the Curie temperature of the recording layer; and at a temperature higher than Tc2, the reproducing layer and the recording layer have maximum total magnetization values, the reproducing device being provided with a light emitting means for emitting light on the magneto-optical recording medium, and a light receiving means for receiving light reflected from the magneto-optical recording medium, wherein upon reproduction, the light emitting means emits light on the magneto-optical recording medium so as to heat the in-plane magnetic layer to more than the Curie temperature.
With this arrangement, at a temperature higher than Tc2, in an area whose temperature is nearly a temperature where total magnetization of the reproducing layer and the total magnetization of the recording layer reach maximum values, the light emitting means performs a heating operation so as to include merely a single bit recorded in the recording layer; thus, leakage flux appearing merely from the bit can be magnetostatically coupled to magnetization of the reproducing layer whose temperature is more than Tc2. Therefore, it is possible to form a large domain in the reproducing layer merely in accordance with a magnetization direction of a single bit that is recorded in the recording layer, so that it is possible to improve the intensity of a signal which is obtained by the light receiving means for receiving light reflected from the magneto-optical recording medium. Consequently, even when a signal is recorded in the recording layer in a period which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce, it is possible to provide a reproducing device which can reproduce the signal without reducing an amplitude of the reproduction signal.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.